1. Field of the Invention
The present invention relates to poly(meth)acrylate polymers, to the plastisols obtainable therefrom and metal sheets coated with the plastisols.
2. Discussion of the Background
Coatings and coverings of polyvinyl chloride (PVC) have occupied a predominant position in the market for many years, by virtue of their suitability for diverse applications and of their good properties during use. Dispersions of PVC powders in plasticizers, otherwise known as plastisols, usually supplemented with stabilizers and possibly with fillers/pigments, are being used on a relatively wide scale for coating, especially in hot-dip processes, for purposes such as corrosion protection of metals and finishing of textiles and leathers, for foamed materials, adhesives, etc. (Savetnik, Plastisols and Organisols, Van Nostrand, New York 1972; W. Becker and D. Braun, Kunststoff-Handbuch [Plastics Manual] (new edition), Vol. 2/2, pp. 1077 et seq., Hanser Verlag 1986).
Plastisols are usually two-phase systems, in which one component is a plastic or mixture of plastics (binder) and the second component is a suitable plasticizer. In principle, binders of the most diverse plastics are conceivable, but only very few plastics have found industrial use. By far the most important class of polymers used for this purpose is derived from polyvinyl chloride (PVC). Because of environmental considerations, however, the use of PVC is questionable. Furthermore, the danger of dioxin formation in a fire situation and of the associated contamination of the surroundings is often prohibitive for the use of PVC.
For this reason, attempts have been made to produce plastisols on the basis of polyacrylates (see German Patent 034498, French Patent A 2291248 and European Patent 0774483 A2).
European Patent 0533026 (Röhm GmbH) describes a plastisol system with an improved adhesion to cataphoretic metal sheets, the system being based on polyalkyl(meth)acrylates and the gellable compound being composed of monomers with an alkyl substituent containing 2 to 12 carbon atoms and of an acid anhydride. No information is disclosed on the abrasion resistance of the obtained plastisol formulations.
German Patent 19814264 (Degussa-Hüls AG) describes improved poly(meth)acrylate plastisols having better storage stability, greater elongation at break and better film-forming properties. No information is disclosed on the abrasion resistance of the obtained plastisols.
European Patent 1162217 (Mitsubishi Rayon Co.) describes a poly(alkyl)methacrylate plastisol composed of primary particles with a diameter greater than 250 mm, the primary particles having a core-shell structure. The obtained plastisols are stable during storage, but information on abrasion resistance is not disclosed.
International Patent 01/21707 (Mitsubishi Rayon Co.) describes finely divided polymers for plastisol production. The polymer particles are characterized by a specific surface of between 0.6 and 20.0 m2/g, determined by nitrogen adsorption. Mechanical data of the obtained plastisols are not disclosed.
Japanese Patent 8295850 (Mitsubishi Rayon Co.) describes a poly(meth)acrylate plastisol with gradient-like structure, wherein the concentration of the unsaturated carboxylic acid and the concentration of the monomer, which is not compatible with the plasticizer, increase from the core to the shell. Mechanical data of the plastisol are not disclosed.
Japanese Patent 11-076855 (Mitsubishi Rayon Co.) describes a core-shell polymer containing functional groups. The functional groups of the core-shell polymer are capable of reacting, at gelling temperature (about 200° C.), with further functional groups of an organic low molecular compound. Mechanical characteristics of the plastisol film are not disclosed.